Here are the major differences between the first edition and the second edition:

a) Lars revised the rendering chapters (Geometry and Coloring, Lighting, and Rasterization) to cover vertex and fragment shaders rather than the old fixed function pipeline.
b) As part of that, we added a simple shader interface in our game engine.
c) We also added a DX9 renderer and more discussion of DX9.
d) I wrote a new chapter about probability, basic statistics and random numbers.
e) The remaining chapters were updated, cleaned up, and rearranged in an order that we think makes a little more sense.

Overall, we think the book is much better and more useful for modern renderer development.

As a side note, I’m still puzzled at the lack of reviews for the second edition. For those reading this, feel free to write one — if you like the book.